Mechanistic insights into the roles of precursor content, synthesis time, and dispersive solvent in maximizing supercapacitance of N-rGO sheets

Graphene oxide (GO) sheets were prepared using the improved Hummers' method, followed by simultaneous reduction and nitrogen doping using an easy solvothermal route to obtain Nitrogen-doped reduced graphene oxide (N-rGO) sheets. The amount of N-doping was controlled using the different amounts of GO and Urea, keeping the ratio of the two (1:3) fixed. Here, we examined several variations in synthesis parameters, viz. change in precursor content, variation in synthesis time, and volume of dispersive solvent. The N-rGO sample prepared with 250 mg GO and 750 mg urea at 24-hour synthesis time in 80 ml dispersive solvent exhibits a superlative specific capacitance of 1244 F/g at 0.5 A/g using 3-electrode measurements in an acidic medium. The high value can be understood via the synergistic roles of optimum defects, degree of reduction, and types of Nenvironments. The symmetric 2-electrode device prepared by depositing the synthesized material onto carbon cloth exhibits supercapacitance of 635 F/g at 1 A/g current density and high cyclic constancy with capacitive retention of similar to 96% after 10000 charge-discharge cycles. Our work provides critical mechanistic insights on the complex intermingling of an optimum N-content, the relative amount of the different N-environments, degree of reduction, and disorder to generate a high specific capacitance, remarkably better than previously reported works on similar materials. Notably, a relatively high graphitic-N, with moderate surface N-content (4.64%) and a moderate degree of reduction, leads to this higher specific capacitance.